Ok, I think I have the trailer figured out...

First, the trailer as shown can only be talking about Khan. Neither Gary Mitchel or Garth of Izar (the two leading challengers for the Big Bad spot apparently) match the attributes of the character depicted in the trailer.

This is how to make the Khan story work within the alt-history of the JJ-verse:

At some point prior to the first film, Khan is discovered by Captain Pike in cryonic hibernation. This allows the use of "Khan's vengence" as the through plot of the film as the voice-over indicates. The back story needn't go much beyond a basic "We found him. He tried to take over. We exiled/imprisoned him...."

Now, consider that the producers have been hinting at a significant death as a key piece of the film. The trailer seems to support this with the memorial service, et al. But, like everything else in the JJ-verse, there must be a twist to it. JJ wouldn't simply do a direct copy of "Wrath...", despite the scenes leaked in the Japanese trailer that would seem to indicate that he is.

However, there's a way to have it both ways:

Pike is the one in the last part of the trailer (the "wall scene"), sacrificing his life to stop Khan. This would allow us to have our "Wrath..." visual tributes, be enough of a twist so as not to be a direct copy of "Wrath..." AND allow Pike to have a tragic fate just as Pike Prime did.

The "consoling" scene with Scotty and Uhura might argue against that (the obvious implication being that Spock is the one to die), BUT could still work in the context of Uhura grieving on Spock's behalf, or for Spock's pain at losing his mentor, Pike.

At some point prior to the first film, Khan is discovered by Captain Pike in cryonic hibernation. This allows the use of "Khan's vengence" as the through plot of the film as the voice-over indicates. The back story needn't go much beyond a basic "We found him. He tried to take over. We exiled/imprisoned him...."

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Problems:

1. No personal connection to Kirk, Spock or any other major character. Mitchell has a personal connection to Kirk, and Garth could too. Inventing a personal connection for Khan requires a convoluted backstory - he got unfrozen, then fell afoul of Kirk, then got imprisoned, and that doesn't even happen on screen? Sounds like you'd need a movie just to do the setup.

3. Any canon character would need to be revamped to explain the Jedi powers, so that doesn't affect the odds of any charatcer one way or the other.

4. Mitchell and Garth are white, Khan is not. Cumby is the right race to play only two of those three. The name Khan also carries expectations that the character is nonwhite. Gary and Garth are as white as it gets.

To revise Khan to fit the needs of a summer popcorn movie would require the same revisions as Mitchell or Garth, but with more complications - how did he get unfrozen and into a Starfleet uniform? Therefore he is less optimal for a summer popcorn movie where explanations must be kept to the bare minimum so we can get to the damn splosions quickly vs the simpler characers who require less explanation.

I've been hoping it's Garth because Cumby would fit the role best, but he's more the right age for Mitchell, so I've pingponged back to the glowy eyed guy.

4. Mitchell and Garth are white, Khan is not. Cumby is the right race to play only two of those three. The name Khan also carries expectations that the character is nonwhite. Gary and Garth are as white as it gets.

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Are folks who's parents come from Spain considered white? I can never keep that straight.

1. No personal connection to Kirk, Spock or any other major character. Mitchell has a personal connection to Kirk, and Garth could too. Inventing a personal connection for Khan requires a convoluted backstory - he got unfrozen, then fell afoul of Kirk, then got imprisoned, and that doesn't even happen on screen? Sounds like you'd need a movie just to do the setup.

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Who says it's a "personal connection"? The goal of the Big Bad in the trailer seems to be revenge on Earth/Starfleet, not any one person.

Same reason he wore one in Space Seed. He was issued a change of clothes from ship's stores. (Presuming that the thing he's shown wearing IS a starfleet uniform and that it is shown in the context of a flashback.

3. Any canon character would need to be revamped to explain the Jedi powers, so that doesn't affect the odds of any charatcer one way or the other.

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Khan is a genetically engineered super soldier like Captain America who has demonstrated similar physical prowess. Furthermore, Gary Mitchel would not need a gun, as the trailer Big Bad is seen to use.

4. Mitchell and Garth are white, Khan is not. Cumby is the right race to play only two of those three. The name Khan also carries expectations that the character is nonwhite. Gary and Garth are as white as it gets.

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Look up "Indo-Aryan" or "Indian Aryan" online. The Aryan bloodline originates FROM India.

To revise Khan to fit the needs of a summer popcorn movie would require the same revisions as Mitchell or Garth, but with more complications - how did he get unfrozen

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Again, 5 lines or less, basically: "We found him. We unfroze him. He tried to take my ship. We ended up exiling him."

and into a Starfleet uniform?

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Also already answered.

Therefore he is less optimal for a summer popcorn movie where explanations must be kept to the bare minimum so we can get to the damn splosions quickly vs the simpler characers who require less explanation.

4. Mitchell and Garth are white, Khan is not. Cumby is the right race to play only two of those three. The name Khan also carries expectations that the character is nonwhite. Gary and Garth are as white as it gets.

.

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Are folks who's parents come from Spain considered white? I can never keep that straight.

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Yeah, the notion that race has anything important to do with Khan is arrant nonsense.

Folks who develop "expectations" about people's backgrounds based on their surnames must live in a frequent state of surprise if not shock.

In response to your quote from the trailer:
"We found him. He tried to take over. We exiled/imprisoned him..."
That actually fits the backstory of Garth.
The race of "shape-shifters" gifted him with their ability to change form because he was so gravely injured, and could have in some way altered him mentally. He ended up turning on them and wanted to destroy them. Naturally his officers turned on him and Garth was inevitably imprisoned/exiled and later deemed insane by Starfleet.
So IMO this quote from the trailer more fits Garth...not Khan.

Let's also not forget that Garth was a fairly lame character (with a pretty silly backstory) in a very bad third season episode of TOS, so unless the new writers have re-imagined the hell out of him, utilizing Garth as the main villain would be a very bad call.

In response to your quote from the trailer:
"We found him. He tried to take over. We exiled/imprisoned him..."
That actually fits the backstory of Garth.
The race of "shape-shifters" gifted him with their ability to change form because he was so gravely injured, and could have in some way altered him mentally. He ended up turning on them and wanted to destroy them. Naturally his officers turned on him and Garth was inevitably imprisoned/exiled and later deemed insane by Starfleet.
So IMO this quote from the trailer more fits Garth...not Khan.

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That quote was not from the trailer. That was a generalized idea from me of how to handle the Khan backstory in film.

And the shapeshifters never gave Garth the sort of "supersoldier" attirbutes that the trailer character displays. Garth was not a one-man weapon as the trailer character is said to be.